1. Field of the Invention
The present invention relates to a laser frequency stabilizing device, laser frequency stabilizing method and laser frequency stabilizing program for changing the resonant cavity length based on a light output signal to stabilize the oscillation frequency of a laser light.
2. Description of the Related Art
A continuous-wave oscillation, 532-nm range solid laser uses a Nd:YAG crystal or the like as a gain medium, which is pumped with a semiconductor laser. The wavelength of such the solid laser is utilized as the standard for lengths. An actual measurement using a wavelength of the laser light requires oscillations of the laser at a single frequency, that is, in a single longitudinal mode.
Further, the use of the laser light wavelength for length measurement requires higher frequency stability of the laser light in order to reduce uncertainty of the length measurement. In an iodine-stabilized laser using an iodine molecular absorption line spectrometry, the oscillation frequency can be controlled at the center of a saturated absorption signal to produce a laser light with high frequency stability (see, for example, Patent Document 1: JP 2001-274495A).
The device in Patent Document 1, however, modulates the resonant cavity length and controls the oscillation frequency of the laser light to capture the saturated absorption signal. Therefore, modulation takes place in the oscillation frequency of the laser light for use in length measurement and so forth. In a word, in the prior art, the influence of the modulation associated with the measurement of the saturated absorption signal may deteriorate the measurement accuracy and so forth as a problem.
To overcome the above problem, there has been proposed a configuration in the art, which includes a modulator such as an electro-optic modulator (EOM). The configuration uses an expensive optical element, which elevates the cost.
Therefore, the present invention has an object to provide a laser frequency stabilizing device, laser frequency stabilizing method and laser frequency stabilizing program capable of eliminating the influence of modulation at lower costs.